Fabrication of 12 µm pixel-pitch 1280 × 1024 extended short wavelength infrared focal plane array using heterojunction type-II superlattice-based photodetectors

Abstract

We present an intial demonstration of a 1280 × 1024 extended short-wavelength infrared focal plane array (FPA) imager with 12 μm pixel-pitch based on type–II InAs/AlSb/GaSb superlattice heterojunction photodetectors, with a novel bandstructure-engineered photo-generated carrier extractor as the window layer in the hetero structure to efficiently extract the photo-generated carriers. This heterostructure with a larger bandgap top window/contact layer leads to the device having lower dark current density compared to conventional pn junction devices. The large format FPA was fabricated with 12 μm pixel-pitch using a developed fabrication process. Test pixels fabricated separately exhibit 100% cut–off wavelengths of ∼2.22, ∼2.34 μm, and ∼2.45 μm at 150, 200 K, and 300 K. The test devices achieve saturated quantum efficiency values under zero bias of 54.3% and 68.4% at 150 and 300 K, under back-side illumination and without any anti-reflection coating. At 150 K, these photodetectors exhibit dark current density of 1.63 × 10−7 A cm−2 under −20 mV applied bias providing a specific detectivity of 1.01 × 1011 cm · Hz1/2/W at 1.9 μm.